Conventional writing tools uses a double-push arrangement, for example Japanese Patent Publication No. 34-7181, to project the tip out of or retract it into the end of the tube.
FIG. 24 is a longitudinal cross-sectional view of the double-push arrangement and FIGS. 25(a) and 25(b) are exploded views for illustration thereof.
FIGS. 24, 25(i a) and 25(b) show a core casing 3 contained in an outer sleeve 2. The outer sleeve 2 has a cylindrical cam 14 fitted or shaped inside a rear portion thereof. The cylindrical cam 14 has some, say three, axial projecting strips 15 separated at an equal angle inside the rear portion thereof, each projecting strip having a shallow groove shape 16a and having a root 17 at an edge thereof.
The conventional writing tools have a push cap 4 provided, which comprises a push cam 18 and a push rod 19. The push cam 18 has six axial strips 20 outside a cylinder portion of the cylindrical cam 14 which are fitted into deep grooves 16b formed between the respective shallow groove 16a of the cylindrical cam 14 and the respective strips 15 thereof. The strips 20 are made to form a crown which a has peaks 21 and roots 22 on an end of the cylinder portion of the cylindrical cam 14. The push rod 19 projects out of a rear end of the outer sleeve 2.
The core casing has a rotation cam 23 fitted in a rear portion thereof. The rotation cam 23 has on an outside thereof axial strips 24 which can be fitted in the deep grooves 16b of the cylindrical cam 14. The strips 24 are made to form a crown which has peaks 25 and roots 26 alternately on an end of the cylindrical portion of the rotation cam 23.
The push rod 19 can be pressed in opposition to a retracting spring (see FIG. 1). The rotation cam 23 and the core casing 3, then, can be pressed in opposition to the retracting spring where slopes of the peaks 25 of the rotation cam 23 are fitted to, but deviate a little from, slopes of the peaks 21 of the push cam 18. The strips 24 of the rotating cam 23, then, can be detached from the deep grooves 16b of the cylindrical cam 23 which is in the state shown in FIG. 25(a). In this state, the retracting spring presses the slopes of the peaks of the rotation cam 23 to the slopes of peaks 21 of the push cam 18. This can revolve the rotation cam 23 to make the respective peaks and respective roots fit. In turn, the slopes of the peaks of the rotation cam 23 press the slopes of the roots 17 of the cylindrical cam 14 to further revolve the rotation cam 23. The respective peaks 25 of the rotation cam 23, then can fit with the respective roots 17 of the cylindrical cam 14 as shown in FIG. 25(b). The end of the core casing 3, thus, can be held projected out of the end of the outer sleeve 2.
In the state shown in FIG. 25(b), when the push rod 19 is pressed again in opposition to the retracting spring, the rotation cam 23 and the core casing 3 can be pressed in opposition to the retracting spring where the slopes of the respective peaks 25 are fitted to, but deviate a little, from the slopes of the respective peaks 21 of the push cam 18. This detaches the peaks 25 of the rotation cam 23 from the roots 17 of the cylindrical cam. This allows the rotation cam 23 to turn, which in turn allows the peaks and roots of the rotation cam 23 to fit with the respective peaks and roots of the push cam 18. In turn the force of the retracting spring makes the slopes of the peaks 25 of the rotation cam 23 press the slopes of the respective roots 17 of the cylindrical cam 14 turn the rotation cam 23. The strips 24 of the rotation cam 23, then, can be pressed in the respective deep grooves 16b of the cylindrical cam 14 as shown in FIG. 25(a). This allows the push rod 19 having the push cam 18 to be retracted. At the same time, the end of the core casing 3 is withdrawn from the end of the outer sleeve 2.
However, the above-described convention writing tools have such serious problems as complicated structure, difficult assembling work, high manufacturing cost and undependability. These difficulties are due to the use of the double-push arrangement comprising the complicated shaped cylindrical cam 14, the push rod 19 having the push cam 18 and the rotation cam 23.